Once a tool used exclusively by mountaineers to secure themselves against deadly falls, the carabiner has been adopted for hundreds of more mundane uses—like carrying housekeys, or strapping a water bottle to your gear with this simple but useful replacement carabiner cap.

It's sized to perfectly replace the cap on your average bottle of water, adding an incredibly useful plastic clippable loop so you can hang it from a pack, your belt, or even your finger. It's also just $4, available in five colors, and promises to do wonders for the environment since it encourages people to re-use and refill a plastic bottle instead of just chucking it.